Precision of intraocular lens power prediction in eyes shorter than 22 mm: An analysis of 6 formulas

Changes in cataract and refractive surgery practice patterns among JSCRS members over the past 20 years

PURPOSE

To evaluate changes in cataract and refractive surgery practice patterns among members of the Japanese Society of Cataract and Refractive Surgery (JSCRS) over the past 20 years.

STUDY DESIGN

Questionnaire survey study.

SUBJECTS AND METHODS

Clinical surveys were conducted annually between February and April from 2004 to 2023. Survey questions covered various areas, including cataract surgical techniques, anesthesia, endophthalmitis prophylaxis, toric and presbyopia-correcting intraocular lenses (IOLs), complications, and refractive surgery.

RESULTS

The highest (n=554 [36.8%]) and lowest (n=316 [19.1%]) numbers of responses were collected in 2012 and 2016, respectively. In perioperative management, the intraoperative use of polyvinyl alcohol-iodine solution and topical antibiotic prescription 3 days before surgery has increased. The use of intracameral injection at the end of surgery has also significantly increased, although it has not been established as common practice. In anesthesia, there is a clear polarization between the use of topical drops and tenon injection. The use of toric IOLs and presbyopia-correcting IOLs has significantly increased from 2010 to 2023. In the latter, the use of trifocal IOLs has particularly increased. Regarding IOL power calculations, the Barrett True K and the Barrett Universal II formulas are rapidly gaining popularity for application with and without post-laser vision correction, respectively. In refractive surgery, phakic IOLs and corneal refractive therapy have attracted considerable interest, followed by laser in situ keratomileusis.

CONCLUSIONS

Evaluation of annual clinical survey data over the past two decades provided valuable insights into the shifting practice patterns and clinical opinions among JSCRS members.

Comparison of Hill-RBF 3.0 with Barrett Universal II, SRK/T, Hoffer Q, Haigis, and Holladay 1 to predict the accuracy of post-cataract surgery refractive outcomes in Indian eyes

PURPOSE

To compare Hill-RBF 3.0 with Barrett Universal II (BU II), SRK/T, Hoffer Q, Haigis, and Holladay 1 in predicting the accuracy of post-cataract surgery refractive outcomes in Indian eyes.

METHODS

In this prospective, comparative, observational study, consecutive patients with uncomplicated age-related cataracts undergoing uneventful phacoemulsification with posterior chamber intraocular lens (IOL) implantation were included. The mean absolute errors (MAEs) and median absolute errors were used to determine the accuracy of predicted postoperative target refractions.

RESULTS

A total of 219 eyes of 173 patients were enrolled. Based on the axial lengths (AL), the patients were classified into: AL <22 mm (short), 22-24.5 mm (normal), and >24.5 mm (long). BU II exhibited the lowest MAE for normal ALs (0.2683 ± 0.2790 D) as well as for the entire population (0.2764 ± 0.2764 D). For the short ALs, Hill RBF 3.0 exhibited the lowest MAE (0.3268 ± 0.3268 D), while for the long ALs, SRK/T showed the lowest MAE (0.2823 ± 0.2642 D). BU II exhibited the highest percentage of eyes of 57.5%, 95.4%, and 98.6% within ±0.25, ±0.75, and ±1.0 D of postoperative target refractions respectively, whereas Hill RBF 3.0 had the highest percentages of eyes (88.1%) within ±0.5 D of postoperative target refraction.

CONCLUSION

Hill-RBF 3.0 exhibited the least MAE for patients with short ALs, while BU II showed the least MAE for normal ALs as well as for the entire population and SRK/T for long ALs. This study is likely to aid surgeons in selecting the most appropriate IOL power formula, which thereby improves the refractive outcomes with utmost accuracy.

Refractive outcomes of immediately sequential bilateral cataract surgery in eyes with long and short axial lengths

PURPOSE

To report the refractive outcomes of long (≥25.00 mm) and short (≤22.00 mm) axial length (AL) eyes undergoing immediately sequential bilateral cataract surgery (ISBCS).

METHODS

In this retrospective cohort study, patients who underwent ISBCS were identified and eyes of patients with bilateral long and short ALs were included. Pre- and postoperative biometry, autorefraction, and ocular comorbidities or complications were recorded. The primary outcome was the mean refractive prediction error.

RESULTS

Thirty-seven patients (74 eyes) with long ALs and 18 patients (36 eyes) with short ALs were included. The means ± standard deviations of the ALs were 26.40 ± 1.38 mm and 21.44 ± 0.46 mm in the long and short AL groups, respectively. In long AL eyes, the mean absolute error from the biometry-predicted refraction was - 0.16 ± 0.46 D, corresponding to 74% of eyes achieving a refraction within ±0.50 D of the predicted value. In short AL eyes, the mean absolute error was - 0.63 ± 0.73 D, corresponding to 44% of eyes achieving a refraction within ±0.50 D of the predicted value. Eight (44.4%) patients with short AL eyes had a myopic deviation greater than ±0.50 D from the predicted result in both eyes.

CONCLUSIONS

Compared to patients with long AL eyes, ISBCS in patients with short ALs had a wider variance in refractive outcome and a lower rate of achieving a postoperative refraction within ±0.50 D of the predicted target.

Comparison of Accuracy of Six Modern Intraocular Lens Power Calculation Formulas

PURPOSE

To compare the accuracy of modern intraocular lens (IOL) power calculation formulas in predicting refractive outcomes after standard cataract surgery.

METHODS

The medical records of 203 eyes from 203 patients that received phacoemulsification and IOL implantation were retrospectively reviewed. Partial coherence interferometry was used to obtain the biometric values. The refractive outcomes of Barrett Universal II (BUII), Emmetropia Verifying Optical (EVO) 2.0, Hill-RBF 3.0, Hoffer QST, Kane, and PEARL-DGS formulas were evaluated. Axial length (AL) subgroup analysis was done separately. The correlations between the prediction error calculated by each formula and AL and corneal power were also analyzed.

RESULTS

Overall, there was no significant difference between the absolute prediction errors predicted by the six formulas after adjusting the mean prediction error (p = 0.058). AL subgroup analysis of absolute error also showed that there is no significant difference between the formulas. The BUII and Hill-RBF 3.0 formulas showed a higher percentage of eyes with prediction error within ±0.50 diopters compared to the Hoffer QST formula (p = 0.022 and p = 0.035, respectively). However, there was no significant difference after Bonferroni correction was applied. The BUII formula showed the highest IOL Formula Performance Index and therefore the highest accuracy, followed by PEARL-DGS, EVO 2.0, Kane, Hill-RBF 3.0, and Hoffer QST formulas. Out of the six formulas, the prediction error calculated by the Hoffer QST was significantly correlated with the AL (p = 0.011). None of the prediction errors calculated by the six formulas showed correlation to the corneal power.

CONCLUSIONS

Analysis of the prediction error showed that the six modern IOL power calculation formulas have comparable accuracy overall and across different ranges of AL.

Influence of miosis and laser peripheral iridotomy on intraocular lens power calculation in patients with primary angle closure disease

OBJECTIVES

To evaluate the effect of miosis and laser peripheral iridotomy (LPI) on intraocular lens (IOL) power prediction and ocular biometry in eyes with primary angle closure disease (PACD).

METHODS

In this prospective observational study, primary angle closure suspects (PACS), and subjects classified with primary angle closure (PAC)/primary angle-closure glaucoma (PACG) undergoing LPI were enrolled. Ocular biometric parameters were measured with IOLMaster700 at baseline (T0), one week after pilocarpine instillation (T1), and another week post LPI (T2). Biometric changes and the IOL power predicted for emmetropia using Barrett Universal II, Haigis, Holladay2, Hoffer Q and SRK/T formulae were analysed and compared among different time points.

RESULTS

100 eyes of 50 PACS and 50 PAC/PACG patients were enrolled. Following pilocarpine-induced miosis, lens thickness (LT) increased and anterior chamber depth (ACD) decreased (all groups p < 0.01), while white-to-white diameter decreased and central corneal thickness increased significantly only in the PACS cohort (both p < 0.01). Compared to baseline, LPI induced an increase of ACD and a slight decrease of LT in PACS (both p < 0.01), whereas only axial length changed significantly (p = 0.012) in the PAC/PACG cohort. Regardless of the formula used, no significant difference to the predicted IOL power for emmetropia existed among the three time points in each group (all p > 0.1).

CONCLUSION

We report the changes of anterior segment parameters induced by miosis and LPI in PACD. These interventions do not significantly affect the IOL power calculation predicted for emmetropia in Chinese eyes when common third-, fourth-and new generation IOL formulae are used.

Recent developments in the intraocular lens formulae: An update

BACKGROUND

The precision of refractive outcomes after uneventful cataract surgery largely depends on the biometry and intraocular lens (IOL) formula used for selecting the IOL. To improve the accuracy of post-op refractive outcomes, several new IOL power calculation formulae have come up. This review would aim to summarise the differences among the new formulae in their performance among normal and variable ocular biometry conditions like short and long axial lengths.

METHODS

A literature review was performed by searching the PubMed and Cochrane databases from 2016 to 2021, identified 483 articles, of which 51 were included in the review.

RESULTS

We identified 15 new IOL formulas (including updates on older formulas) of which, only 8 newer formulas (BUII, Hill-RBF 2.0, Kane, Pearl DGS, LSF AI, Naesar 2, EVO 2.0 and VRF) met the eligibility criteria. They were compared according to the reported median absolute error, mean absolute error and percentage of eyes within 0.5D.

CONCLUSION

The Kane formula and Barrett Universal-II formula performed better than other formulas over the entire axial length (AL) spectrum. In the long eye (AL > 26.0 mm) sub-group, the Kane formula was the most accurate, while in the short eye (AL < 22.0 mm) sub-group, both Kane and EVO 2.0 formulas fared better than other formulas.

Intraocular Lens Formula Comparison of Flanged Intrascleral Intraocular Lens Fixation with Double Needle Technique

Purpose

To analyze visual outcomes and accuracy of intraocular lens (IOL) calculation formulas in predicting postoperative outcomes in patients undergoing flanged intrascleral IOL fixation.

Design

Case Series.

Subjects

Twenty-three patients who had undergone secondary IOL placement using flanged intrascleral fixation technique.

Methods

Retrospective chart review.

Main Outcome Measures

Corrected distance visual acuity (CDVA) and postoperative spherical equivalent based on manifest refraction.

Results

Visual acuity improved from 20/577 to 20/58. Overall, the actual refraction was 0.06 D more myopic than predicted. Holladay 2, Sanders Retzlaff Kraff/Theoretical (SRK/T) and Barrett Universal II resulted in mild myopic surprise (-0.55, -0.18 and -0.20 D). Haigis and Hill-RBF (Radial Basis Function) resulted in mild hyperopic surprise (+0.28 and +0.28 D). Hoffer Q and Holladay 1 were the most accurate (-0.02D and -0.08 D).

Conclusion

Flanged intrascleral IOL fixation improved vision even in patients with other posterior segment pathologies. The effective lens positioning is likely similar to in-the-bag positioning. Hoffer Q and Holladay 1 formulas with in-the-bag calculations were the most accurate.

Treatment of Nanophthalmos Cataracts: Surgery and Complications

PURPOSE

Cataract surgery in patients with nanophthalmos is complicated for ophthalmologists to perform. Due to the unique ocular anatomy, there is a high incidence of complex complications such as angle-closure glaucoma, fluid misdirection syndrome, and uveal effusion syndrome (UES) in the perioperative period of cataract surgery. This article will discuss the management options for cataract surgery in nanophthalmic eyes and complications.

METHODS

This review is searched through PubMed, focusing on articles published in the past 20 years. Articles were reviewed on the anatomical structure of nanophthalmic cataracts, the pathogenesis of complications, the selection of intraocular lenses, and surgical methods.

CONCLUSION

There is a strong correlation between abnormal ocular anatomy and complications in patients with nanophthalmos. Clinicians must not only select the appropriate intraocular lens formula based on the depth of the anterior chamber but also formulate personalized surgical methods based on its unique anatomical structure to avoid complications.

Accuracy of intraocular lens power calculation formulae in short eyes: A systematic review and meta-analysis

This review article attempts to evaluate the accuracy of intraocular lens power calculation formulae in short eyes. A thorough literature search of PubMed, Embase, Cochrane Library, Science Direct, Scopus, and Web of Science databases was conducted for articles published over the past 21 years, up to July 2021. The mean absolute error was compared by using weighted mean difference, whereas odds ratio was used for comparing the percentage of eyes with prediction error within ±0.50 diopter (D) and ±1.0 D of target refraction. Statistical heterogeneity among studies was analyzed by using Chi-square test and I² test. Fifteen studies including 2,395 eyes and 11 formulae (Barrett Universal II, Full Monte method, Haigis, Hill-RBF, Hoffer Q, Holladay 1, Holladay 2, Olsen, Super formula, SRK/T, and T2) were included. Although the mean absolute error (MAE) of Barrett Universal II was found to be the lowest, there was no statistically significant difference in any of the comparisons. The median absolute error (MedAE) of Barrett Universal II was the lowest (0.260). Holladay 1 and Hill-RBF had the highest percentage of eyes within ±0.50 D and ±1.0 D of target refraction, respectively. Yet their comparison with the rest of the formulae did not yield statistically significant results. Thus, to conclude, in the present meta-analysis, although lowest MAE and MedAE were found for Barrett Universal II and the highest percentage of eyes within ±0.50 D and ±1.0 D of target refraction was found for Holladay 1 and Hill-RBF, respectively, none of the formulae was found to be statistically superior over the other in eyes with short axial length.

Comparing the accuracy of new intraocular lens power calculation formulae in short eyes after cataract surgery: a systematic review and meta-analysis

PURPOSE

Calculating the intraocular lens (IOL) power in short eyes for cataract surgery has been a challenge. A meta-analysis was conducted to identify, among several classic and new IOL power calculation formulae, which obtains the best accuracy.

METHODS

All studies aiming at comparing the accuracy of IOL power calculation formulae in short eyes were searched up in the databases of PubMed, EMBASE, Web of Science and the Cochrane library from Jan. 2011 to Mar. 2021. Primary outcomes were the percentages of eyes with a refractive prediction error in ± 0.25D, ± 0.5D and ± 1.0D.

RESULTS

Totally 1,476 eyes from 14 studies were enrolled in comparison of 13 formulae (Barrett Universal II, Castrop, Haigis, Hoffer Q, Holladay1, Holladay2, Kane, Ladas Super Formula, Okulix, Olsen, Pearl-DGS, SRK/T and T2). Pearl-DGS had the highest percentage within ± 0.25D. In the ± 0.5D range, Pearl-DGS obtained the highest percentage again, and it was significantly higher than Barrett Universal II, Haigis, Hoffer Q, Holladay1, Holladay2 and Olsen (P = 0.001, P = 0.02, P = 0.0003, P = 0.01, P = 0.007, P = 0.05, respectively). In the ± 1.0D range, Okulix possessed the highest percentage, and it was significantly higher than Barrett Universal II, Castrop, Hoffer Q and Holladay2 (P = 0.0005, P = 0.03, P = 0.003, P = 0.02, respectively).

CONCLUSION

The new generation formulae, based on artificial intelligence or ray-tracing principle, are more accurate than the convergence formulae. Pearl-DGS and Okulix are the two most accurate formulae in short eyes.

Comparison of the Barrett Universal II formula to previous generation formulae for paediatric cataract surgery

PURPOSE

To compare the accuracy of the Barrett Universal II (BUII) five-variable formula to previous generation formulae in calculating intraocular lens (IOL) power following paediatric cataract extraction.

METHODS

Retrospective study of consecutive paediatric patients who underwent uneventful cataract extraction surgery along with in-the-bag IOL implantation between 2012 and 2018 in the Hospital for Sick Children, Toronto, Ontario, Canada. The accuracy of five different IOL formulae, including the BUII, Sanders-Retzlaff-Kraff Theoretical (SRK/T), Holladay I, Hoffer Q and Haigis, was evaluated. Constant optimization was performed for each IOL and for each formula separately. Mean prediction error (PE) and the mean and median absolute PE (APE) were calculated for the five different IOL formulae investigated.

RESULTS

Sixty-six eyes of 66 children (59% males) with a median age at surgery of 6.2 years (IQR, 3.2-9.2 years) were included in the study. The mean IOL power that was implanted was 23.3 ± 5.1 D (range; 12.0-39.0 D). Overall, the BUII had a comparable median APE to the Hoffer Q, Holladay I, SRK/T and Haigis formulae (BUII: 0.49D versus 0.48D, 0.61D, 0.74D and 0.58D respectively; p = 0.205). The BUII, together with Hoffer Q, produced better predictability within 0.5D from target refraction compared with the SRK/T formula (BUII:51.5%, Hoffer Q:51.5% versus SRK/T:31.8%, p = 0.002 for both).

CONCLUSION

The BUII formula had comparable accuracy to other tested formulae and outperformed the SRK/T formula, when calculating IOL power within the 0.5D range from target refraction in paediatric eyes undergoing cataract surgery with in-the-bag IOL implantation.

[Cataract surgery and the small eye: relative anterior microphthalmos, high hyperopia and nanophthalmos]

Relativer anteriorer Mikrophthalmus, hochgradige Hyperopie und Nanophthalmus bezeichnen klein gebaute Augen mit unterschiedlichem morphologischem Verhältnis zwischen Vorderabschnitt und Achsenlänge. Im Rahmen dieses Beitrags werden intraoperative Herausforderungen und chirurgische Lösungsansätze für die Kataraktoperation bei Patienten mit einer der 3 genannten morphologischen Veränderungen diskutiert. Zusätzlich wird auf mögliche, vorliegende Komorbiditäten, wie z. B. das Glaukom, und die präoperative Planung eingegangen.

Accuracy of the Barrett Universal II formula integrated into a commercially available optical biometer when using a preloaded single-piece intraocular lens

Purpose:

To compare the commonly used formulas for intraocular lens (IOL) selection using IOLMaster^®700 (Carl Zeiss Meditec) and to evaluate the Barrett Universal II (BU-II) formula accuracy when using the Vivinex™ iSert^® XY1 IOL (Hoya Corporation Medical Division).

Methods:

A retrospective chart review was performed that included patients who underwent uneventful cataract surgery with in-the-bag insertion of Vivinex™ iSert^® XY1 IOL. Prediction errors at 3 months postoperative of IOLMaster^® 700 with Haigis, Holladay 1, SRK/T, and BU-II formulas were compared. As a subgroup analysis, we focused on the axial length (AL) and IOL power. AL subgroup analysis was based on the following AL subgroups: short (<22.5 mm), medium (22.5–25.5 mm), and long (>25.5 mm). IOL power subgroup analysis was based on the following IOL power subgroups: low (≤18.0 diopters [D]), medium (18.5–24.0 D), and high (≥24.5 D).

Results:

This study included 590 eyes of 590 patients. Overall, the four IOL calculation formulas appeared to be similarly accurate. In the long AL subgroup, the BU-II formula had a significantly lower absolute error (AE) than the Holladay 1 formula. In the low-power subgroup, the BU-II formula had a significantly lower AE than the Holladay 1 and SRK/T formulas. On the other hand, in the high-power subgroup, the BU-II formula was significantly less accurate than the SRK/T formula and also appeared to be worse than the Holladay 1 formula (P = 0.052).

Conclusion:

The BU-II formula might be less accurate when using a Vivinex™ iSert^® XY1 IOL of 24.5 D or greater.

Optimizing lens constants specifically for short eyes: Is it essential?

Purpose:

Optimization of lens constants is a critically important step that improves refractive outcomes significantly. Whether lens constants optimized for the entire range of axial length would perform equally well in short eyes is still a matter of debate. The aim of this study was to analyze whether lens constants need to be optimized specifically for short eyes.

Methods:

This retrospective observational study was conducted at a tertiary care hospital in Central India. Eighty-six eyes of eighty-six patients were included. Optical biometry with IOLMaster 500 was done in all cases and lens constants were optimized using built-in software. Barrett Universal II, Haigis, Hill-RBF, Hoffer Q, Holladay 1, and SRK/T formulae were compared using optimized constants. Mean absolute error, median absolute error (MedAE), and percentage of eyes within ±0.25, ±0.50, ±1.00, and ±2.00 diopter of the predicted refraction, of each formula were analyzed using manufacturer’s, ULIB, and optimized lens constants. MedAE was compared across various constants used by Wilcoxon signed-rank test and among optimized constants by Friedman’s test. Cochran’s Q test compared the percentage of eyes within ± 0.25, ±0.50, ±1.00, and ± 2.00 diopter of the predicted refraction. A value of P < 0.05 was considered statistically significant.

Results:

Optimized constant of Haigis had significantly lower MedAE (P < 0.00001) as compared to manufacturers. However, there was no statistically significant difference between ULIB and optimized constants. Postoptimization, there was no statistically significant difference among all formulae.

Conclusion:

Optimizing lens constants specifically for short eyes gives no added advantage over those optimized for the entire range of axial length.

Evaluating newer generation intraocular lens calculation formulas in manual versus femtosecond laser-assisted cataract surgery

AIM

To determine the refractive accuracy of the Haigis, Barrett Universal II (Barrett), and Hill-radial basis function 2.0 (Hill-RBF) intraocular lens (IOL) power calculations formulas in eyes undergoing manual cataract surgery (MCS) and refractive femtosecond laser-assisted cataract surgery (ReLACS).

METHODS

This was a REB-approved, retrospective interventional comparative case series of 158 eyes of 158 patients who had preoperative biometry completed using the IOL Master 700 and underwent implantation of a Tecnis IOL following uncomplicated cataract surgery using either MCS or ReLACS. Target spherical equivalence (SE) was predicted using the Haigis, Barrett, and Hill-RBF formulas. An older generation formula (Hoffer Q) was included in the analysis. Mean refractive error (ME) was calculated one month postoperatively. The lens factors of all formulas were retrospectively optimized to set the ME to 0 for each formula across all eyes. The median absolute errors (MedAE) and the proportion of eyes achieving an absolute error (AE) within 0.5 diopters (D) were compared between the two formulas among MCS and ReLACS eyes, respectively.

RESULTS

Of the 158 eyes studied, 64 eyes underwent MCS and 94 eyes underwent ReLACS. Among MCS eyes, the MedAE did not differ between the formulas (P=0.59), however among ReLACS eyes, Barrett and Hill-RBF were more accurate (P=0.001). Barrett and Hill-RBF were both more likely to yield AE<0.5 D among both groups (P<0.001).

CONCLUSION

The Barrett and Hill-RBF formula lead to greater refractive accuracy and likelihood of refractive success when compare to Haigis in eyes undergoing ReLACS.

Comparison of various intraocular lens formulas using a new high-resolution swept-source optical coherence tomographer

PURPOSE

To compare vergence, artificial intelligence, and combined intraocular lens (IOL) calculation formulas using a new swept-source optical coherence tomographer (SS-OCT) and to analyze their performance based on manifest and estimated refractive outcomes of cataract surgery.

SETTING

Department of Ophthalmology, University of Pécs Medical School, Pécs, Hungary.

DESIGN

Retrospective data analysis.

METHODS

Optical biometry readings of patients who underwent uneventful cataract removal and implantation of a monofocal acrylic IOL were used to predict IOL power with Barrett Universal II (BUII), Haigis, Hoffer Q, Holladay 1, Radial Basis Function (RBF) 2.0, Kane, Ladas Super Formula, and SRK/T. All the implanted IOLs were calculated by using the Haigis formula. The arithmetic prediction error and median and mean absolute refractive errors for all formulas were computed. The percentage of eyes within ±0.25 diopters (D), ±0.50 D, and ±1.0 D of prediction error was calculated.

RESULTS

A total of 95 eyes of 95 patients with a mean age of 68.80 ± 7.57 years were included. There was a statistically significant difference in absolute prediction error across the 8 IOL calculation formulas (P < .0001). Haigis showed the lowest mean absolute error, and it differed significantly from the BUII, Hoffer Q, Holladay 1, Ladas, RBF 2.0, and SRK/T formulas (P < .05). In terms of eyes within ±0.25 D, ±0.50 D, and ±1.0 D of prediction error, the Haigis formula showed the overall best performance.

CONCLUSIONS

The results indicated that a recently developed SS-OCT provided accurate ocular biometry measurements before cataract surgery, and the Haigis formula incorporated in its software enabled precise calculation of IOL refractive power.

Clinical Accuracy of 18 IOL Power Formulas in 241 Short Eyes

PURPOSE

To analyze the accuracy of 18 intraocular lens (IOL) power calculation formulas in eyes with axial length (AL) ≤ 22 mm.

METHODS

We analyzed 241 eyes of 241 patients. Eighteen formulas were evaluated: Barrett Universal II (BUII), EVO 2.0, Haigis, Hoffer Q, Holladay 1 and 2, Cooke K6, Kane, LadasSuperFormula AI, Naeser 2, Olsen, Panacea, Pearl-DGS, RBF 2.0, SRK/T, T2, VRF and VRF-G. Optical biometry was performed with an IOLMaster 700 (Carl Zeiss Meditec, Jena, Germany). With lens constants optimized for the whole range of AL, the mean prediction error (PE) and its standard deviation (SD), the median absolute error (MedAE), the mean absolute error (MAE) and the percentage of eyes with PEs within ±0.25 D, ±0.50 D and <±1.00 D were calculated.

RESULTS

Post-hoc analysis of the absolute PE revealed statistically significant differences (P < .05) between some of the newer formulas (K6, Kane, Naeser 2, Olsen and VRF-G), which obtained the lowest MedAE (respectively, 0.308, 0.300, 0.277, 0.310 and 0.276 D) and the remaining ones. These formulas yielded also the highest percentage of eyes with a PE within ±0.50 D (70.54%, 72.20%, 71.37%, 70.95% and 73.03%, respectively), whereas Panacea and SRK/T yielded the lowest percentage (62.24%), with a stastically significant difference (P < .05) with respect to most formulas.

CONCLUSION

In eyes with AL ≤22.0 mm, new formulas (K6, Kane, Naeser 2, Olsen and VRF-G) offer the most accurate predictions of postoperative refraction.

Accuracy of intraocular lens power calculation in primary angle-closure disease: comparison of 7 formulas

PURPOSE

To assess the accuracy of intraocular lens power calculation formulas Barrett Universal II (BUII), Hill-Radial Basis Function (RBF) 3.0, Kane, Ladas Super Formula (LSF), Haigis, Hoffer Q, and SRK/T in primary angle-closure disease (PACD).

METHODS

A total of 129 PACD eyes were enrolled. Prediction refraction was calculated for each formula and compared with actual refraction. Accuracy was determined by formula performance index (FPI), median absolute error (MedAE) and percentage of eyes with a prediction error (PE) within ± 0.50D. Subgroup analysis was performed according to axial length (AL).

RESULTS

Overall, FPI was ranked as follows: Kane (0.067), RBF 3.0 (0.064), Haigis (0.062), SRK/T (0.060), BUII (0.058), Hoffer Q (0.055), and LSF (0.049). Kane got the highest (71.3%) percentage of eyes with PE within ± 0.50 D. In medium AL eyes (22 mm < AL ≤ 25 mm), FPI ranked the same as in total group. MedAEs were equal across all formulas (P = 0.121). In short eyes (AL ≤ 22 mm), FPI was Kane (0.055), RBF 3.0 (0.050), SRK/T (0.050), Haigis (0.049), BUII (0.047), Hoffer Q (0.045), and LSF (0.033). MedAEs were significantly different across all formulas (P = 0.033). Haigis showed the lowest MedAE (0.35 D), Haigis and Kane got the highest percentage (63.6%) of eyes with PE within ± 0.50 D.

CONCLUSION

Kane outperformed in total PACD eyes; RBF 3.0, Haigis, and SRK/T achieved satisfying performance. When dealing with PACD eyes shorter than 22 mm, Kane achieved the best accuracy. RBF 3.0, SRK/T, Haigis, and BUII achieved comparable outcomes. No formula showed superiority over others for medium AL PACD eyes.

Comparison of accuracy of different intraocular lens power calculation methods using artificial intelligence

PURPOSE

To assess the accuracy of the intraocular lens (IOL) power calculation based on three methods using artificial intelligence (AI) and one formula using no AI.

METHODS

During cataract surgery on 114 eyes, one type of IOL was implanted, calculated with the Hill-RBF 2.0 method. The theoretical postoperative refractions were calculated using the Kane and the Pearl-DGS methods and a vergence based formula (Barrett Universal II, BUII). The differences between the manifest and objective postoperative refractions and the predicted refractions were calculated. The percentage of eyes within ±0.5 D and ±1.0 D prediction error (PE), the mean, and the median absolute errors (MAE and MedAE) were also determined.

RESULTS

The mean age of the patients was 69.48 years; the axial length was between 21.19 and 25.39 mm. The number of eyes within ±0.5/±1.0 D PE was 96/108 (84.21%/94.73%) using the Hill-RBF 2.0 method, 92/107 (80.70%/93.85%) with the Kane method, 91/107 (79.82%/93.85%) with the Pearl-DGS method, and 91/106 (79.82%/92.98%) with the BUII formula, using subjective refraction. With objective refractometric data, PEs were within ±0.5 D in 88 (77.19%), 83 (72.80%), 82 (71.92%), and 80 (70.17%) cases (Hill-RBF, Kane, Pearl-DGS, BUII, respectively). MAE and MedAE were also best with the Hill-RBF 2.0 method (0.3 D; 0.18 D).

CONCLUSION

Better accuracy of PE might be obtained by the Hill-RBF 2.0 method compared with BUII. The Kane and Pearl-DGS methods showed similar accuracy when compared with BUII.

Recent developments in intraocular lens power calculation methods-update 2020

For many decades only a few formulas have been available to calculate the intraocular lens (IOL) power for patients undergoing cataract surgery: the Haigis, Hoffer Q, Holladay 1 and 2 and SRK/T. In recent years, several new formulas for IOL power calculation have been introduced with the aim of improving the accuracy of refraction prediction in eyes undergoing cataract surgery. These include the Barrett Universal II, the Emmetropia Verifying Optical (EVO), the Kane, the Næser 2, the Olsen, the Panacea, the Pearl DGS, the Radial Basis Function (RBF), the T2 and the VRF formulas. Although most of them are unpublished so that their structure is unknown, we give an overview of each formula and report the results of the studies that have compared them. Their performance in short and long eyes is provided and a special focus is given on the issue of segmented axial length, which is a promising method to obtain more accurate outcomes in short and long eyes. Here, the group refractive index originally developed for the IOLMaster may not represent the best method to convert the optical path length into a physical distance. The issue of posterior and total corneal astigmatism (TCA) is discussed in relation to toric IOLs; the latest formulas for toric IOLs and their results are also reported.

Bilateral implantation of +56 and +58 diopter custom-made intraocular lenses in patient with extreme nanophthalmos

Purpose

To present the case of a 60-year-old patient with severe nanophthalmic eyes, who underwent cataract surgery with a bilateral implantation of custom-made high-power intraocular lenses (IOLs).

Observations

The axial length was 14.94 and 15.05 mm of the right and the left eye, respectively. The preoperative corrected distance visual acuity (CDVA) was +0.46 logMAR (20/63) in the right eye and +0.58 logMAR (20/80) in the left eye with rigid contact lenses of +17.5 D bilaterally. The calculated IOL power for emmetropia with different formulas ranged from +55.28 to +70.09 D. The IOL power selection was based on the average value from four formulas (Haigis, Holladay 1, Holladay 2, SRK/T) with the target refraction of emmetropia. Custom-made +56.0 and + 58.0 D Aspira-aAY IOLs (HumanOptics AG, Erlangen, Germany) were implanted without any complications. The postoperative CDVA was +0.40 logMAR (20/50) and +0.60 logMAR (20/80). The manifest refraction spherical equivalents were +0.625 D and −0.375 D.

Conclusions and importance

Even in eyes with the axial length of only 15 mm, cataract surgery can be successfully performed after adequate preparation. High-power customized IOLs allow complete correction of hyperopia but caution is required with the results from different IOL power calculation formulas, which can be misleading.

Accuracy of common IOL power formulas in 611 eyes based on axial length and corneal power ranges

AIMS

To provide clinical guidance on the use of intraocular lens (IOL) power calculation formulas according to the biometric parameters.

METHODS

611 eyes that underwent cataract surgery were retrospectively analysed in subgroups according to the axial length (AL) and corneal power (K). The predicted residual refractive error was calculated and compared to evaluate the accuracy of the following formulas: Haigis, Hoffer Q, Holladay 1 and SRK/T. Furthermore, the percentages of eyes with ≤±0.25, ≤±0.5 and 1 dioptres (D) of the prediction error were recorded.

RESULTS

The Haigis formula showed the highest percentage of cases with ≤0.5 D in eyes with a short AL and steep K (90%), average AL and steep cornea (73.2%) but also in long eyes with a flat and average K (65% and 72.7%, respectively). The Hoffer Q formula delivered the lowest median absolute error (MedAE) in short eyes with an average K (0.30 D) and Holladay 1 in short eyes with a steep K (Holladay 1 0.24 D). SRK/T presented the highest percentage of cases with ≤0.5 D in average long eyes with a flat and average K (80.5% and 68.1%, respectively) and the lowest MedAE in long eyes with an average K (0.29 D).

CONCLUSION

Overall, the Haigis formula shows accurate results in most subgroups. However, attention must be paid to the axial eye length as well as the corneal power when choosing the appropriate formula to calculate an IOL power, especially in eyes with an unusual biometry.

Ratio of Axial Length to Corneal Radius in Japanese Patients and Accuracy of Intraocular Lens Power Calculation Based on Biometric Data

PURPOSE

To evaluate the features of the axial length-to-corneal radius (AL/CR) ratio in Japanese patients with cataracts and to determine the accuracy of intraocular lens (IOL) power calculation formulas according to the AL/CR features and the axial length (AL).

DESIGN

Retrospective observational case series.

METHODS

Setting was a clinical practice. Patient population was a total of 1,135 eyes (1,135 patients) with cataracts. Observation procedures included measurement of the AL and corenal radius (CR) by optical biometry and evaluation of the refractive outcomes by using the SRK/T, Holladay 1, Hoffer Q, Haigis, and Barrett Universal II formulas. Main outcome measurements were the features of the AL/CR ratio and the accuracy of IOL power calculations based on the AL/CR ratio and the AL.

RESULTS

The mean AL/CR ratio was 3.15 ± 0.19. Significant weak negative correlations were observed between the spherical equivalent (SE) and AL (r = -0.7489; P < .001) and between the SE and AL/CR ratio (r = -0.8069; P < .001); no correlation was found between the SE and CR (r = 0.0208, P = .483). For medium ALs and high AL/CR ratios, the SRK/T formula performed less accurately. For long ALs and high AL/CR ratios, the Holladay 1 and Hoffer Q formulas performed less accurately. The Barrett Universal II formula performed well across a range of ALs and AL/CR ratios.

CONCLUSIONS

The AL/CR ratio explained the total variation in the SE better than the AL alone. Surgeons should pay attention to the selection of IOL power calculation formulas in eyes with high AL/CR ratios.

Intraocular Lens Power Formulas, Biometry, and Intraoperative Aberrometry: A Review

The refractive outcome of cataract surgery is influenced by the choice of intraocular lens (IOL) power formula and the accuracy of the various devices used to measure the eye (including intraoperative aberrometry [IA]). This review aimed to cover the breadth of literature over the previous 10 years, focusing on 3 main questions: (1) What IOL power formulas currently are available and which is the most accurate? (2) What biometry devices are available, do the measurements they obtain differ from one another, and will this cause a clinically significant change in IOL power selection? and (3) Does IA improve refractive outcomes? A literature review was performed by searching the PubMed database for articles on each of these topics that identified 1313 articles, of which 166 were included in the review. For IOL power formulas, the Kane formula was the most accurate formula over the entire axial length (AL) spectrum and in both the short eye (AL, ≤22.0 mm) and long eye (AL, ≥26.0 mm) subgroups. Other formulas that performed well in the short-eye subgroup were the Olsen (4-factor), Haigis, and Hill-radial basis function (RBF) 1.0. In the long-eye group, the other formulas that performed well included the Barrett Universal II (BUII), Olsen (4-factor), or Holladay 1 with Wang-Koch adjustment. All biometry devices delivered highly reproducible measurements, and most comparative studies showed little difference in the average measures for all the biometric variables between devices. The differences seen resulted in minimal clinically significant effects on IOL power selection. The main difference found between devices was the ability to measure successfully through dense cataracts, with swept-source OCT-based machines performing better than partial coherence interferometry and optical low-coherence reflectometry devices. Intraoperative aberrometry generally improved outcomes for spherical and toric IOLs in eyes both with and without prior refractive surgery when the BUII and Hill-RBF, Barrett toric calculator, or Barrett True-K formulas were not used. When they were used, IA did not result in better outcomes.

Development of a new intraocular lens power calculation method based on lens position estimated with optical coherence tomography

A new method is developed and validated for intraocular lens (IOL) power calculation based on paraxial ray tracing of the postoperative IOL positions, which are obtained with the use of anterior segment optical coherence tomography. Of the 474 eyes studied, 137 and 337 were grouped into training and validation sets, respectively. The positions of the implanted IOLs of the training datasets were characterized with multiple linear regression analyses one month after the operations. A new regression formula was developed to predict the postoperative anterior chamber depth with the use of the stepwise analysis results. In the validation dataset, postoperative refractive values were calculated according to the paraxial ray tracing of the cornea and lens based on the assumption of finite structural thicknesses with separate surface curvatures. The predicted refraction error was calculated as the difference of the expected postoperative refraction from the spherical-equivalent objective refraction values. The percentage error (within ±0.50 diopters) of the new formula was 84.3%. This was not significantly correlated to the axial length or keratometry. The developed formula yielded excellent postoperative refraction predictions and could be applicable to eyes with abnormal proportions, such as steep or flat corneal curvatures and short and long axial lengths.

Accuracy of the Hill-radial basis function method and the Barrett Universal II formula

PURPOSE

The aim was to assess the postoperative results of a biometric method using artificial intelligence (Hill-radial basis function 2.0), and data from a modern formula (Barrett Universal II) and the Sanders-Retzlaff-Kraft/Theoretical formula.

METHODS

Phacoemulsification and biconvex intraocular lens implantation were performed in 186 cataractous eyes. The diopters of intraocular lens were established with the Hill-radial basis function method, based on biometric data obtained using the Aladdin device. The required diopters of the intraocular lens were also calculated by the Barrett Universal II formula and with the Sanders-Retzlaff-Kraft/Theoretical formula. The differences between the manifest postoperative refractive errors and the planned refractive errors were calculated, as well as the percentage of eyes within ±0.5 D of the prediction error. The mean- and the median absolute refractive errors were also determined.

RESULTS

The mean age of the patients was 70.13 years (SD = 10.67 years), and the mean axial length was 23.47 mm (range = 20.72-28.78 mm). The percentage of eyes within a prediction error of ±0.5 D was 83.62% using the Hill-radial basis function method, 79.66% with the Barrett Universal II formula, and 74.01% in the case of the Sanders-Retzlaff-Kraft/Theoretical formula. The mean- and the median absolute refractive errors were not statistically different.

CONCLUSION

Clinical success was the highest when using the biometric method, based on pattern recognition. The results obtained using Barrett Universal II came a close second. Both methods performed better compared to a traditionally used formula.

Visual And Refractive Outcomes In Hyperopic Pseudophakic Patients Implanted With A Trifocal Intraocular Lens

Purpose

To assess visual and refractive results after bilateral implantation of a trifocal intraocular lens (IOL) in patients with hyperopia.

Methods

In a retrospective nonrandomized study, 196 eyes of 98 patients had bilateral implantation of a trifocal IOL. The Barrett Universal II formula was used for IOL power calculation. Eyes were divided into two groups for their analysis: low-moderate, with IOL power ranging from 22 to 26 D, and high, with IOL power ranging from 25 to 34 D. Refractive error was used to assess predictability, and corrected distance visual acuity (CDVA) and uncorrected distance visual acuity values were used to assess efficacy and safety of the surgery.

Results

Six months postoperatively, our results revealed a Snellen decimal CDVA of 0.97±0.05 and 0.94±0.09, for the low-moderate and high groups, respectively. The low-moderate hyperopia group showed a 75.23% of eyes with 20/20 of CDVA and 100% of eyes with 20/25 of CDVA, and the high hyperopia group showed 60.95% and 94.29% for these values of visual acuity, respectively. The mean postoperative spherical equivalent was -0.25±0.36D and -0.24±0.42D for low-moderate and high hyperopia groups, respectively. In the case of low-moderate hyperopia group, 81% of eyes were within ±0.50D and 99% within ±1.00D. These values were 78% and 95%, respectively, for the high hyperopic eyes.

Conclusion

Bilateral implantation of a trifocal IOL in hyperopic eyes provided good visual and refractive outcomes. The Barrett Universal II formula was accurate in predicting the IOL power in hyperopic eyes.

Improving clinical refractive results of cataract surgery by machine learning

AIM

To evaluate the potential of the Support Vector Machine Regression model (SVM-RM) and Multilayer Neural Network Ensemble model (MLNN-EM) to improve the intraocular lens (IOL) power calculation for clinical workflow.

BACKGROUND

Current IOL power calculation methods are limited in their accuracy with the possibility of decreased accuracy especially in eyes with an unusual ocular dimension. In case of an improperly calculated power of the IOL in cataract or refractive lens replacement surgery there is a risk of re-operation or further refractive correction. This may create potential complications and discomfort for the patient.

METHODS

A dataset containing information about 2,194 eyes was obtained using data mining process from the Electronic Health Record (EHR) system database of the Gemini Eye Clinic. The dataset was optimized and split into the selection set (used in the design for models and training), and the verification set (used in the evaluation). The set of mean prediction errors (PEs) and the distribution of predicted refractive errors were evaluated for both models and clinical results (CR).

RESULTS

Both models performed significantly better for the majority of the evaluated parameters compared with the CR. There was no significant difference between both evaluated models. In the ±0.50 D PE category both SVM-RM and MLNN-EM were slightly better than the Barrett Universal II formula, which is often presented as the most accurate calculation formula.

CONCLUSION

In comparison to the current clinical method, both SVM-RM and MLNN-EM have achieved significantly better results in IOL calculations and therefore have a strong potential to improve clinical cataract refractive outcomes.

New Approach for the Calculation of the Intraocular Lens Power Based on the Fictitious Corneal Refractive Index Estimation

Purpose

To identify the sources of error in predictability beyond the effective lens position and to develop two new thick lens equations.

Methods

Retrospective observational case series with 43 eyes. Information related to the actual lens position, corneal radii measured with specular reflection and Scheimpflug-based technologies, and the characteristics of the implanted lenses (radii and thickness) were used for obtaining the fictitious indexes that better predicted the postoperative spherical equivalent (SE) when the real effective lens position (ELP) was known. These fictitious indexes were used to develop two thick lens equations that were compared with the predictability of SRK/T and Barrett Universal II.

Results

The SE relative to the intended target was correlated to the difference between real ELP and the value estimated by SRK/T (ΔELP) (r = -0.47, p=0.002), but this only predicted 22% of variability in a linear regression model. The fictitious index for the specular reflection (n _k) and Scheimpflug-based devices (n _c) were significantly correlated with axial length. Including both indexes fitted to axial length in the prediction model with the ΔELP increased the r-square of the model up to 83% and 39%, respectively. Equations derived from these fictitious indexes reduced the mean SE in comparison to SRK/T and Barrett Universal II.

Conclusions

The predictability with the trifocal IOL evaluated is not explained by an error in the ELP. An adjustment fitting the fictitious index with the axial length improves the predictability without false estimations of the ELP.